Optical device with variable wavelength interference filter

ABSTRACT

An optical device includes a telecentric optical system, a variable wavelength interference filter, and a detection section, the variable wavelength interference filter includes a first reflecting film, a second reflecting film provided to a movable section, and an electrostatic actuator adapted to displace the movable section, an effective measurement area capable of transmitting a light with a wavelength, which is within a predetermined allowable range centered on a measurement center wavelength when an amount of the displacement of the movable section takes a maximum displacement value, is set in the first reflecting film and the second reflecting film, and the telecentric optical system guides the incident light to the variable wavelength interference filter so that a principal ray of the incident light is parallel thereto and perpendicular to the first reflecting film, and at the same time, collects the incident light in the effective measurement area.

BACKGROUND

1. Technical Field

The invention relates to an optical device provided with a variablewavelength interference filter for taking out light with a predeterminedwavelength from incident light.

2. Related Art

In the past, there has been known an interference filter having a pairof reflecting films opposed to each other, and for transmitting orreflecting only the light with a predetermined wavelength, which isreinforced due to multiple interference by the pair of reflecting films,out of the incident light, and further, there has been known an opticaldevice for imaging the light transmitted through such an interferencefilter with an image sensor (see, e.g., JP-A-2000-162043 (Document 1)).

The optical device described in Document 1 is a device for collimatingthe incident light such as the light from an object with an objectivelens, inputting the light thus collimated vertically to a variablewavelength interference filter, and receiving and then imaging the lighttransmitted through the variable wavelength interference filter with animage sensor.

In such an optical device, it is required to improve the resolution ofthe variable wavelength interference filter in order for receiving thelight with a target wavelength using the image sensor. As such avariable wavelength interference filter, there can be cited, forexample, a filter shown in JP-A-2009-251105 (Document 2).

The variable wavelength interference filer described in Document 2 has apair of substrates opposed to each other, and one of the substrates isprovided with a movable section and a diaphragm for holding the movablesection so as to be able to move back and forth with respect to theother of the substrates. Further, the movable section is provided withone of the pair of reflecting films, and the other of the substrates notprovided with the movable section is provided with the other of thereflecting films opposed to the reflecting film of the movable section.In such an optical filter device, the dimension of the gap between thepair of reflecting films can be varied by moving back and forth themovable section to thereby make it possible to take out the lightcorresponding to the dimension of the gap, and at the same time, sincean amount of deflection of the movable section with respect to thediaphragm is reduced, it becomes possible to suppress also thedeflection of the reflecting film provided to the movable section.

Incidentally, in Document 2, since the movable section is formed to havea thickness dimension larger than that of the diaphragm, it is possibleto make the deflection amount of the movable section smaller than thedeflection amount of the diaphragm even in the case in which the movablesection is displaced. However, in reality, the deflection is also causedin the movable section, and the deflection amount is small in thecentral portion of the movable section, and increases as the positionmoves from the center toward the periphery of the movable section.Further, the deflection amount is also affected by the size of thevariable wavelength interference filter, if the size of the variablewavelength interference filter is large, for example, the deflectionamount of the movable section becomes also large. Therefore, since thedeflection is also caused in the reflecting film disposed on the movablesection, and the dimension of the gap between the pair of reflectingfilms fails to be uniform, the resolution is degraded.

Therefore, in the optical device described in Document 1, if thevariable wavelength interference filter described above is used, therearises a problem that the measurement accuracy is degraded due to thedegradation of the resolution in the variable wavelength interferencefilter. Further, although it is possible to obtain an image with higherresolution by increasing the size of the image sensor, on this occasion,it is required to also increase the size of the variable wavelengthinterference filter. However, as described above, if the size of thevariable wavelength interference filter is increased, there arises aproblem that the deflection amount of the movable section increases tothereby degrade the resolution, and thus the measurement accuracy isdegraded.

SUMMARY

An advantage of some aspects of the invention is to provide an opticaldevice capable of highly accurate spectroscopic measurement.

An aspect of the invention is directed to an optical device including avariable wavelength interference filter adapted to transmit a lightreinforced by multiple interference out of an incident light, atelecentric optical system adapted to guide the incident light to thevariable wavelength interference filter, and a detection section adaptedto detect a light transmitted through the variable wavelengthinterference filter, wherein the variable wavelength interference filterincludes a first substrate, a second substrate opposed to the firstsubstrate and provided with a movable section, and a holding sectionadapted to hold a periphery of the movable section and to hold themovable section so as to allow a back and forth movement of the movablesection with respect to the first substrate, a first reflecting filmprovided to the first substrate, a second reflecting film provided tothe movable section, and opposed to the first reflecting film via a gap,and a gap varying section adapted to displace the movable section tothereby vary a dimension of the gap, an effective measurement areacapable of transmitting a light with a wavelength, which is within apredetermined allowable range centered on a measurement centerwavelength when an amount of the displacement of the movable section dueto the gap varying section takes a maximum value, is set in the firstreflecting film and the second reflecting film, and the telecentricoptical system guides a principal ray of the incident lightperpendicularly to one of a plane of the first reflecting film and aplane of the second reflecting film, and collects the incident light inthe effective measurement area.

In this aspect of the invention, the telecentric optical system is animage side telecentric optical system, and guides the light so that theprincipal ray of the light emitted from the telecentric optical systemis parallel to the optical axis and perpendicular to the variablewavelength interference filter. Further, the telecentric optical systemcollects light so that the principal ray is collected in the effectivemeasurement area out of the gap region formed between the firstreflecting film and the second reflecting film of the variablewavelength interference filter. It should be noted that the telecentricoptical system denotes the optical system arranged so that the principalray passes through the focal point, namely the optical system in whichthe principal ray is parallel to the optical axis, namely the fieldangle is 0 degree. Further, the image side telecentric optical systemdenotes the optical system which becomes parallel to the principal rayand the optical axis on the image side.

Here, the effective measurement area denotes the area where thedegradation of the resolution of the variable wavelength interferencefilter can be suppressed within a allowable range. Specifically, thelight on which the multiple interference is caused in the effectivemeasurement area and transmitted through the effective measurement areaout of the gap region between the first reflecting film and the secondreflecting film becomes the light with the wavelength within theallowable wavelength range centered on the measurement centerwavelength.

Therefore, by collecting the principal ray in the effective measurementarea of the variable wavelength interference filter using thetelecentric optical system, it is possible to accurately take out thelight with the wavelength within the wavelength range centered on themeasurement center wavelength from the incident light to make thedetection section receive the light. Thus, the degradation of theresolution in the variable wavelength interference filter can besuppressed compared to the case of, for example, inputting the parallellight to the variable wavelength interference filter and taking out thelight using also the area of the gap region outside the effectivemeasurement area, and thus the highly accurate spectroscopic measurementcan be performed in the optical device.

In the optical device of the above aspect of the invention, it ispreferable that the effective measurement area is an area where adifference value between a dimension of the gap along a center axis ofthe movable section and a dimension of the gap corresponding aperipheral edge of the effective measurement area is one of equal to andsmaller than a half of the allowable range if the amount of thedisplacement of the movable section is set to the maximum displacementvalue by the gap varying section.

In this configuration, assuming that the difference between the gapdimension corresponding to the point on the center axis of the movablesection and the gap dimension corresponding to the peripheral edge ofthe effective measurement area in the condition of displacing themovable section as much as the maximum displacement amount using the gapvarying section is “x,” and the allowable range is “λ₀,” the area wherethe relationship of x=λ₀/2 is fulfilled is defined as the effectivemeasurement area.

Specifically, in the variable wavelength interference filter, thedimension “d” of the gap and the transmission wavelength “λ” areexpressed as d=λ/2 assuming that the refractive index of the air is 1.Therefore, assuming that the gap dimension on the center axis of themovable section is “d₁,” and the gap dimension corresponding to theperipheral edge of the effective measurement area is “d₂,” thewavelength (the measurement center wavelength) of the light transmittedthrough the center axis of the movable section becomes λ₁=2d₁, and thewavelength of the light transmitted through the peripheral edge of theeffective measurement area becomes λ₂=2d₂=2(d₁+x)=2(π₁/2+x).

Here, the wavelength range within the allowable range λ₀ centered on themeasurement center wavelength λ₁ becomes the range from λ₁−λ₀ to λ₁+λ₀.If the movable section is deflected toward the first substrate, there isno chance for the gap dimension to be smaller than d₁, and therefore, ifthe wavelength λ₂(=2(λ/2+x)) of the light transmitted through theperipheral edge of the effective measurement area is equal to or smallerthan λ₁+λ₀, then the light transmitted through the effective measurementarea becomes the light having the wavelength within the allowable rangeλ₀ centered on the measurement center wavelength λ₁. Therefore, bycollecting the incident light in the effective measurement area wherex≦λ₀/2 is fulfilled using the telecentric optical system, it becomespossible to make the detection section detect only the light having thewavelength within the allowable range λ₀ from the measurement centerwavelength λ₁.

In the optical device of the above aspect of the invention, it ispreferable that there is further provided a magnifying lens systemdisposed between the variable wavelength interference filter and thedetection section, and adapted to magnify the light transmitted throughthe variable wavelength interference filter.

According to this configuration, since there is adopted a configurationof collecting the incident light using the telecentric optical system,it is possible to make a contribution to the downsizing of the variablewavelength interference filter. In addition thereto, by providing themagnifying lens system, it is possible to magnify the light transmittedthrough the variable wavelength interference filter, and then emit thelight toward the detection section. According to such a configuration,the size of the detection section alone can be enlarged withoutenlarging the size of the variable wavelength interference filter, andit is possible to further improve the detection accuracy.

In the optical device of the above aspect of the invention, it ispreferable that there is further provided a first circularly polarizingplate disposed between the telecentric optical system and the variablewavelength interference filter, and adapted to transmit a lightproceeding from the telecentric optical system toward the variablewavelength interference filter, and absorb a light proceeding from thevariable wavelength interference filter toward the telecentric opticalsystem.

In this configuration, the first circularly polarizing plate is disposedbetween the variable wavelength interference filter and the telecentricoptical system.

In general, in the variable wavelength interference filter, the light onwhich the multiple interference is caused between the first reflectingfilm and the second reflecting film and is reinforced is transmittedtoward the detection section, and the light component fails to betransmitted is mostly reflected toward the entrance side. If such areflected component returns to the telecentric optical system, thereflected component is further reflected inside the lens and between thelenses to cause ghost or flare, and the detection accuracy in thedetection section is degraded.

In contrast, according to the configuration of the invention, the firstcircularly polarizing plate can prevent the light reflected by thevariable wavelength interference filter from returning to thetelecentric optical system to thereby prevent the ghost or the moirefringes from occurring, thus the detection accuracy in the detectionsection can be improved.

In the optical device of the above aspect of the invention, it ispreferable that there is further provided a second circularly polarizingplate disposed between the variable wavelength interference filter andthe detection section, and adapted to transmit a light proceeding fromthe variable wavelength interference filter toward the detectionsection, and absorb a light proceeding from the detection section towardthe variable wavelength interference filter.

According to this configuration, the second circularly polarizing plateis disposed between the variable wavelength interference filter and thedetection section, and it is possible to prevent the problem that thelight reflected by the detection section returns to the variablewavelength interference filter, and then further makes the mirrorreflection to return to the detection section.

Further, it is also possible to use both of the first circularlypolarizing plate and the second circularly polarizing plate, and in sucha case, the polarization direction of the linearly polarizing plate ofthe first circularly polarizing plate and the polarization direction ofthe linearly polarizing plate of the second circularly polarizing plateare aligned to each other. Thus, it is possible to prevent the lightreflected by the variable wavelength interference filter from returningto the telecentric optical system, and to prevent the light reflected bythe detection section from returning to the detection section via thevariable wavelength interference filter, and thus the detection accuracycan further be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a diagram showing a schematic configuration of an opticaldevice according to a first embodiment of the invention.

FIG. 2 is a cross-sectional view showing a schematic configuration of avariable wavelength interference filter according to the firstembodiment.

FIG. 3 is an enlarged view of the part indicated by the dashed-twodotted line A shown in FIG. 2 in the condition in which a voltage isapplied between a first electrode and a second electrode to therebyfully deflect the movable section toward a first substrate.

FIG. 4 is a diagram showing light paths of light beams guided by atelecentric optical system in the optical device according to the firstembodiment.

FIG. 5 is a diagram showing a rough outline of the shape of the lightbeam emitted from the telecentric optical system.

FIG. 6 is a diagram showing the peak wavelength variation of the lighttransmitted through the variable wavelength interference filter withrespect to the tilt of a principal ray.

FIG. 7 is a diagram showing light paths of light beams guided by atelecentric optical system of the optical device according to a secondembodiment of the invention.

FIG. 8 is a diagram showing light paths of light beams guided by atelecentric optical system of the optical device according to a thirdembodiment of the invention.

FIG. 9 is a diagram showing light paths of light beams guided by atelecentric optical system of the optical device according to a fourthembodiment of the invention.

FIG. 10 is a diagram showing another example of the telecentric opticalsystem.

DESCRIPTION OF EXEMPLARY EMBODIMENTS First Embodiment

A first embodiment of the invention will hereinafter be explained withreference to the accompanying drawings.

1. Overall Configuration of Optical Device

FIG. 1 is a diagram showing a schematic configuration of an opticaldevice 1 according to the present embodiment of the invention.

As shown in FIG. 1, the optical device 1 is provided with an opticalsensor 3, and a control device 4. Further, the optical device 1 is aspectroscopic camera device, which is a device for shooting the image ofa measurement object 2 with a detection section 32, and then measuringthe dispersed light intensity distribution characteristics.

2. Configuration of Optical Sensor

As shown in FIG. 1, the optical sensor 3 is provided with a variablewavelength interference filter 5, a telecentric optical system 31 forguiding the light to the variable wavelength interference filter 5, thedetection section 32 for receiving the light transmitted through thevariable wavelength interference filter 5, and a voltage control circuit33 for varying the wavelength of the light to be transmitted through thevariable wavelength interference filter 5.

2-1. Configuration of Variable Wavelength Interference Filter

FIG. 2 is a cross-sectional view showing a schematic configuration ofthe variable wavelength interference filter.

As shown in FIG. 2, the variable wavelength interference filter 5 isprovided with a first substrate 51 and a second substrate 52. These twosubstrates 51, 52 are each made of a material capable of transmittingthe light in the visible range such as a variety of types of glassincluding, for example, soda glass, crystalline glass, quartz glass,lead glass, potassium glass, borosilicate glass, and alkali-free glass,or quartz crystal. Further, these two substrates 51, 52 are integrallyconfigured by bonding the bonding surfaces 513, 523 formed along therespective peripheral edges to each other with a plasma-polymerized film53 consisting primarily of, for example, siloxane.

Further, between the first substrate 51 and the second substrate 52,there are disposed a first reflecting film 56 and a second reflectingfilm 57. Here, the first reflecting film 56 is fixed to a surface of thefirst substrate 51 opposed to the second substrate 52, and the secondreflecting film 57 is fixed to a surface of the second substrate 52opposed to the first substrate 51. Further, the first reflecting film 56and the second reflecting film 57 are disposed so as to be opposed toeach other via a gap. Here, the space sandwiched between the firstreflecting film 56 and the second reflecting film 57 is referred to as agap region. Further, the variable wavelength interference filter 5causes multiple interference in the incident light in the gap region tothereby transmit the reinforced light.

Further, between the first substrate 51 and the second substrate 52,there is disposed an electrostatic actuator 54 as a gap varying sectionaccording to the invention. The electrostatic actuator 54 is constitutedby a first electrode 541 provided to the first substrate 51 and a secondelectrode 542 provided to the second substrate 52.

2-1-1. Configuration of First Substrate

An electrode groove 511 and a mirror fixation section 512 are formed onthe opposed surface of the first substrate 51 opposed to the secondsubstrate 52 using an etching process.

Although not shown in the drawing, the electrode groove 511 is formed tohave a ring shape centered on the center point of the plane in a planview of the first substrate 51 viewed in a substrate thicknessdirection.

The mirror fixation section 512 is formed to have a cylindrical shapecoaxial with the electrode groove 511 and projecting toward the secondsubstrate 52.

On the bottom surface of the electrode groove 511, there is formed thefirst electrode 541 having a ring-like shape constituting theelectrostatic actuator 54. Further, the first electrode 541 is providedwith a first electrode line (not shown), which is extending along awiring groove, and is formed toward the periphery of the first substrate51. Further, the tip of the first electrode line is connected to avoltage control circuit 33.

Further, on the surface of the mirror fixation section 512 opposed tothe second substrate 52, there is fixed the first reflecting film 56.The first reflecting film 56 can be a dielectric multilayer filmcomposed of layers made of, for example, SiO₂ and TiO₂ stacked on eachother, or a film formed of a metal film made of, for example, an Agalloy. Further, the configuration of stacking both of the dielectricmultilayer film and the metal film can also be adopted.

Further, in an area of the surface of the first substrate outside theelectrode groove 511, there is formed a first bonding surface 513. Asdescribed above, the first bonding surface 513 is provided with theplasma-polymerized film 53 for bonding the first substrate 51 and thesecond substrate 52 to each other.

2-1-2. Configuration of Second Substrate

The second substrate 52 has a surface not opposed to the first substrate51 formed by being processed using an etching process. The secondsubstrate 52 is provided with a movable section 521 having a cylindricalshape centered on the center point of the substrate, and a holdingsection 522 coaxial with the movable section 521 and for holding themovable section 521. Here, the holding section 522 is formed to have adimension of the external diameter identical to the dimension of theexternal diameter of the electrode groove 511 of the first substrate 51.

The movable section 521 is formed to have a thickness dimension largerthan that of the holding section 522 in order for preventing thedeflection.

The holding section 522 is a diaphragm surrounding the periphery of themovable section 521, and is formed to have a thickness dimension of, forexample, 50 μm. It should be noted that although the holding section 522shaped like a diaphragm is shown as an example in the presentembodiment, it is also possible to adopt, for example, a configurationprovided with a holding section having a plurality of pairs of beamstructures disposed at positions symmetrical about the center of themovable section.

The surface of the holding section 522 opposed to the first substrate 51is provided with a second electrode 542 having a ring-like shape andopposed to the first electrode 541 with a predetermined gap. Here, asdescribed above, the second electrode 542 and the first electrode 541described above constitute the electrostatic actuator 54.

Further, a second electrode line (not shown) is formed from a part ofthe peripheral edge of the second electrode 542 toward the periphery ofthe second substrate 52, and the tip of the second electrode line isconnected to a voltage control circuit 33.

On the surface of the movable section 521 opposed to the first substrate51, there is formed the second reflecting film 57 opposed to the firstreflecting film 56 via a gap. It should be noted that the configurationof the second reflecting film 57 is the same as that of the firstreflecting film 56, and therefore, the explanation here will be omitted.

2-1-3. Operation of Variable Wavelength Interference Filter WhenApplying Voltage and Effective Measurement Area

FIG. 3 is an enlarged view of the part indicated by the dashed-twodotted line A shown in FIG. 2 in the condition in which a voltage isapplied between the first electrode 541 and the second electrode 542 tothereby fully deflect the movable section 521 toward the first substrate51.

In the initial state shown in FIG. 2, when the voltage control circuit33 applies a drive voltage between the first electrode 541 and thesecond electrode 542, the movable section 521 of the second substrate 52is displaced toward the first substrate 51 due to the electrostaticattractive force as shown in FIG. 3.

In this case, although the movable section 521 is formed to have athickness dimension larger than that of the holding section 522 shapedlike a diaphragm, and therefore, has a shape difficult to deflect,minute deflection occurs in reality due to the deflection of the holdingsection 522. Here, the amount of deflection of the movable section 521increases as the distance from the center axis O of the movable section521 increases. Therefore, in the periphery of the movable section 521,the dimension of the gap between the second reflecting film 57 formed onthe movable section 521 and the first reflecting film 56 opposed theretoalso increases. On this occasion, a difference in the peak wavelength iscaused between the light transmitted through a part of the gap regionlocated on the center axis O of the movable section 521 and the lighttransmitted through the peripheral part of the gap region, and thus theresolution of the variable wavelength interference filter 5 is degraded.

The difference in the peak wavelength described above is required to besuppressed within a previously determined allowable range in order forimprove the detection accuracy in the detection section 32. In theembodiment of the invention, a part of the gap region where thedifference in the peak wavelength can be suppressed within the allowablerange is defined as an effective measurement area G, and the incidentlight is collected within the effective measurement area G (the areabetween the dashed-dotted lines of the surfaces of the first reflectingfilm 56 and the second reflecting film 57 shown in FIGS. 2 and 3) usingthe telecentric optical system 31. Thus, the detection section 32 ismade to detect only the light transmitted through the effectivemeasurement area G.

Here, assuming that the effective measurement area G is an area capableof transmitting the light with a wavelength within an allowable value λ₀from the measurement center wavelength λ₁ of the light transmittedthrough the area on the center axis O of the movable section 521, theeffective measurement area G corresponds to the area where the amount ofdeflection of the movable section 521 in the thickness direction isequal to or smaller than λ₀/2 in the condition in which the movablesection 521 is fully displaced toward the first substrate 51.Specifically, assuming that the gap dimension on the center axis O ofthe movable section 521 is d₁, and the gap dimension in the peripheraledge of the effective measurement area G is d₂, Formula (1) below istrue.d ₂ −d ₁=λ₀/2  (1)

Further, the allowable value λ₀ is appropriately determined inaccordance with the purpose of the optical device 1, and is preferablyset equal to or smaller than 5 nm in the case of measuring thedispersion spectrum distribution of the visible range as a typical imagesensor, for example, and is preferably set equal to or smaller than 10nm in the case of using infrared light. Therefore, in the variablewavelength interference filter 5, it is preferable to set the area,where the amount of deflection is equal to or smaller than 2.5 through 5nm in the case of fully displacing the movable section 521, as theeffective measurement area G.

2-2. Configuration of Telecentric Optical System

The telecentric optical system 31 is an optical system for guiding theincident light from the measurement object 2 to the variable wavelengthinterference filter 5, and is composed of a plurality of opticalcomponents such as a lens.

FIG. 4 is a diagram showing light paths of light beams guided by thetelecentric optical system 31. FIG. 5 is a diagram showing a roughoutline of the shape of the light beam emitted from the telecentricoptical system 31.

The telecentric optical system 31 guides the light input from a range (afield angle), which can be imaged by the optical device 1, to thevariable wavelength interference filter 5 via a plurality of lenses.Here, the telecentric optical system 31 converts the light input fromthe object to the optical device 1 into a light beam having a conicalshape shown in FIG. 5. Further, the telecentric optical system 31 emitsthe light so that the principal ray of the light is parallel to theoptical axis, and is perpendicular to the first substrate 51 (the firstreflecting film 56) of the variable wavelength interference filter 5.Further, the telecentric optical system 31 guides the light input to thefield angle range, which can be imaged, so as to be collected to theinside of the effective measurement area G of the variable wavelengthinterference filter 5.

It should be noted that “perpendicular” described here includes theangle with which no difference in the peak wavelength is caused in thelight transmitted through the variable wavelength interference filter 5as well. FIG. 6 is a diagram showing the peak wavelength variation ofthe light transmitted through the variable wavelength interferencefilter with respect to the tilt of the principal ray. In FIG. 6, it isassumed that the one-sided gradient of the light beam having a conicalshape input to the variable wavelength interference filter is set to 5degrees as shown in FIG. 5.

As shown in FIG. 6, the peak wavelength of the light transmitted throughthe variable wavelength interference filter 5 varies significantly asthe variation in the incident angle increases. Further, the variation inthe peak wavelength also increases as the wavelength increases.Therefore, in the lens design of the telecentric optical system 31,setting can preferably be performed in accordance with how muchvariation in the peak wavelength can be allowed with respect to thewavelength band desired to be transmitted through the variablewavelength interference filter 5.

For example, in the case of inputting the light of 1100 nm into thevariable wavelength interference filter 5, if the incident angle isshifted 2.7 degree, the variation of 1 nm is caused in the peakwavelength. Therefore, when making the variable wavelength interferencefilter 5 perform dispersion on the wavelength band equal to or shorterthan 1100 nm, if the variation in the peak wavelength due to theincident angle of the principal ray is desired to be suppressed to alevel equal to or smaller than 1 nm, it is required to suppress the tiltof the principal ray of the light beam emitted from the telecentricoptical system 31 to a level no larger than 2.7 degree.

2-3. Configuration of Detection Section

Returning to FIG. 1, the detection section 32 is disposed on the focalplane of the telecentric optical system 31, and the image light of theimage inside the field angle is guided by the telecentric optical system31, and is formed as an image on the detection section 32 and then takenas an image by the detection section 32.

The detection section 32 is provided with a plurality of detectionelements (not shown) arranged as an array. These detection elements areformed of photoelectric conversion elements such as charge coupleddevices (CCD), and generate electric signals corresponding to the lightintensity of the light received, then output the electric signals to thecontrol device 4. The detection section 32 is disposed on the focalplane of the telecentric optical system 31.

2-4. Configuration of Voltage Control Circuit

The voltage control circuit 33 controls the voltages appliedrespectively to the first electrode 541 and the second electrode 542 ofthe electrostatic actuator 54 in accordance with the control of thecontrol device 4.

3. Configuration of Control Device

The control device 4 controls overall operations of the optical device1.

The control device 4 is a computer composed mainly of a storage section41, and a central processing unit (CPU) 42, and for example, ageneral-purpose computer, a portable information terminal, and acomputer dedicated to measurement can be used.

Further, the control device 4 is provided with a drive control section421, a light intensity obtaining section 422, and an intensitydistribution measurement section 423 as the software executed on the CPU42.

The storage section 41 stores various programs performed on the CPU 42and various data. Further, the storage section 41 stores correlationdata representing the wavelength of the transmitted light detected bythe detection section 32 with respect to the drive voltage applied tothe electrostatic actuator 54.

Then, the drive control section 421, the light intensity obtainingsection 422, and the intensity distribution measurement section 423 asthe software executed on the CPU 42 will be explained.

The drive control section 421 obtains a voltage value (an input value)with which the detection section 32 can receive the measurement objectlight based on the correlation data stored in the storage section 41,and then output the voltage value thus obtained to the voltage controlcircuit 33 to thereby vary the distance of the gap of the variablewavelength interference filter 5.

The light intensity obtaining section 422 obtains the intensity of thereceived light detected by each of the detection elements of thedetection section 32. The intensity of the received light thus obtainedis stored in the storage section 41 in conjunction with the positiondata of the detection elements.

The intensity distribution measurement section 423 creates a lightintensity distribution map based on the light intensity of themeasurement object light detected by each of the detection elements thusobtained by the light intensity obtaining section 422.

For example, the intensity distribution measurement section 423 createsthe light intensity distribution map having pixels corresponding to thecoordination positions of the respective detection elements, and sets acolor, a gray value, and so on of each of the pixels in accordance withthe intensity of the light received by the detection elementcorresponding to the pixel.

Action and Advantages of First Embodiment

The optical device 1 according to the first embodiment described aboveis provided with the variable wavelength interference filter 5, thetelecentric optical system 31 for guiding the incident light to thevariable wavelength interference filter 5, and the detection section 32.Further, the telecentric optical system 31 is an image side telecentricoptical system, and emits the light beam having the principal rayparallel to the optical axis and perpendicular to the plane of the firstreflecting film 56 toward the variable wavelength interference filter 5.Further, the telecentric optical system 31 inputs the incident lightwithin the range of the field angle to the effective measurement area Gwhere the wavelength of the transmitted light is within the allowablevalue λ₀ from the measurement center wavelength λ₁.

Specifically, assuming that the gap dimension on the center axis O ofthe movable section 521 is d₁, the telecentric optical system 31 inputthe incident light within the field angle range in the area where thegap dimension d₂ fulfills d₁≦d₂<d₁+λ₀ in the condition in which themovable section 521 is fully displaced.

Therefore, the variable wavelength interference filter 5 can transmitthe light having the wavelength within the allowable range λ₀ centeredon the measurement center wavelength, and thus the resolution can beimproved. Further, by receiving such transmitted light by the detectionsection 32, accurate measurement of the spectral characteristics of theimage light can be performed, and thus the measurement accuracy can beimproved.

Second Embodiment

A second embodiment of the invention will now be explained withreference to the accompanying drawings.

FIG. 7 is a diagram showing light paths of light beams guided by atelecentric optical system of the optical device according to the secondembodiment of the invention.

As shown in FIG. 7, in the optical device 1A of the second embodiment, afirst circularly polarizing plate 34 is disposed between the telecentricoptical system 31 and the variable wavelength interference filter 5 inthe optical device 1 of the first embodiment.

The first circularly polarizing plate 34 is composed of a linearlypolarizing plate 341 facing to the telecentric optical system 31 and a¼-wave plate 342 facing to the variable wavelength interference filter 5combined with each other.

In such a first circularly polarizing plate 34, the linearly polarizingplate 341 transmits only, for example, the P-polarized wave and absorbsthe S-polarized wave out of the light input from the telecentric opticalsystem 31. Further, the ¼-wave plate 342 converts the P-polarized wavethus transmitted into the circularly polarized light (the right-handedcircularly polarized wave), and then emits it toward the variablewavelength interference filter 5.

Incidentally, in the variable wavelength interference filter 5, thelight reinforced by the multiple interference is transmitted toward thedetection section 32 as the transmitted light, while the light with theother wavelengths are almost reflected toward the telecentric opticalsystem 31.

On this occasion, the reflected light is reversed in the rotationdirection. For example, since in the present embodiment, the conversioninto the right-handed circularly polarized wave is performed by the¼-wave plate 342, the reflected light becomes the left-handed circularlypolarized wave. When entering the ¼-wave plate 342 of the firstcircularly polarizing plate 34, such a left-handed circularly polarizedwave is converted into the S-polarized wave, then absorbed by thelinearly polarizing plate 341, but not transmitted toward thetelecentric optical system 31.

Action and Advantages of Second Embodiment

In the optical device 1A according to the second embodiment describedabove, the first circularly polarizing plate 34 is disposed between thetelecentric optical system 31 and the variable wavelength interferencefilter 5, and the first circularly polarizing plate 34 is composed ofthe linearly polarizing plate 341 facing to the telecentric opticalsystem 31 and the ¼-wave plate 342 facing to the variable wavelengthinterference filter 5 combined with each other.

Therefore, the first circularly polarizing plate 34 can transmit theincident light from the telecentric optical system 31 toward thevariable wavelength interference filter 5, and absorb the lightreflected by the variable wavelength interference filter 5. Thus, thereis no chance for the light reflected by the variable wavelengthinterference filter 5 to return to the telecentric optical system 31,and thus, the moire fringes or the ghost caused by such a reflected wavebeing reflected inside the lens or between the lenses of the telecentricoptical system can also be prevented from occurring. Therefore, thedegradation of the light intensity measurement accuracy in the detectionsection 32 can be prevented.

Third Embodiment

Then, an optical device according to a third embodiment of the inventionwill be explained with reference to the accompanying drawings.

FIG. 8 is a diagram showing a schematic configuration of an opticaldevice 1B according to the third embodiment.

As shown in FIG. 8, in the optical device 1B of the third embodiment, asecond circularly polarizing plate 35 is further disposed between thevariable wavelength interference filter 5 and the detection section 32in the optical device 1A of the second embodiment.

The second circularly polarizing plate 35 is composed of a ¼-wave plate351 facing to the variable wavelength interference filter 5 and alinearly polarizing plate 352 facing to the detection section 32combined with each other. Here, the linearly polarizing plate 352 hasthe same polarization direction as that of the linearly polarizing plate341 of the first circularly polarizing plate 34, and transmits theP-polarized wave.

The right-handed circularly polarized wave is input to the variablewavelength interference filter 5 due to the first circularly polarizingplate 34. Further, in the second circularly polarizing plate 35, the¼-wave plate 351 converts the right-handed circularly polarized wavetransmitted through the variable wavelength interference filter 5 intothe linearly polarized light (P-polarized wave). The linearly polarizedlight is transmitted through the linearly polarizing plate 352, and isemitted toward the detection section 32.

Meanwhile, the light component reflected by the detection section 32 istransmitted through the second circularly polarizing plate 35, and isreflected by the variable wavelength interference filter 5. Thereflected light is absorbed by the linearly polarizing plate 352 of thesecond circularly polarizing plate 35, and is prevented from returningto the detection section 32.

Action and Advantages of Third Embodiment

In the optical device 1B according to the third embodiment describedabove, the second circularly polarizing plate 35 is disposed between thevariable wavelength interference filter 5 and the detection section 32,and the second circularly polarizing plate 35 is composed of the ¼-waveplate 351 facing to the variable wavelength interference filter 5 andthe linearly polarizing plate 352 facing to the detection section 32combined with each other.

Therefore, the second circularly polarizing plate 35 can transmit theincident light from the variable wavelength interference filter 5 towardthe detection section 32, and absorb the light reflected by thedetection section 32. Thus, since there is no chance for the lightreflected by the detection section 32 to return to the variablewavelength interference filter 5, and therefore there is no chance forthe multiple interference to be caused again in such reflected wave inthe gap of the variable wavelength interference filter 5, thedegradation of the light intensity measurement accuracy in the detectionsection 32 can be prevented.

Fourth Embodiment

Then, an optical device 1C according to a fourth embodiment of theinvention will be explained with reference to the accompanying drawings.

FIG. 9 is a diagram showing a schematic configuration of the opticaldevice 1C according to the fourth embodiment.

As shown in FIG. 9, the optical device 1C according to the fourthembodiment is a modification of the optical device 1B according to thethird embodiment, and has a magnifying lens system 36 disposed betweenthe second circularly polarizing plate 35 and the detection section 32.

Further, in the optical device 1C, the variable wavelength interferencefilter 5 is disposed on the focal plane of the telecentric opticalsystem 31, and the detection section 32 is disposed on the focal planeof the magnifying lens system 36.

In such an optical device 1C, the light transmitted through the variablewavelength interference filter 5 is magnified by the magnifying lenssystem 36, and is then detected by the detection section 32. Accordingto such a configuration, the size of the detection section 32 can be setlarger with respect to the size of the variable wavelength interferencefilter 5, and thus the high-resolution image can be obtained with alarger number of detection elements. Therefore, more accurate anddetailed spectral distribution measurement can be performed.

In other words, in the optical devices 1, 1A, and 1B of the first,second, and third embodiments, it is required to set the size of theeffective measurement area G in the variable wavelength interferencefilter 5 and the size of the detection section 32 roughly the same aseach other. Therefore, if the size of the detection section 32 isenlarged, it is necessary to enlarge also the size of the variablewavelength interference filter 5.

Here, since in the present invention the effective measurement area Gwith which the degradation of the resolution is within the allowablerange is set, it is necessary to enlarge the size of the effectivemeasurement area G in accordance with the detection section 32 so as tocorrespond to the size of the detection section 32. However, if the sizeof the variable wavelength interference filter 5 is enlarged in orderfor enlarging the size of the effective measurement area G, the amountof the deflection of the movable section 521 is increased in accordancewith the amount of the enlargement. Therefore, there is a problem thatthere arises a necessity of setting the amount of the enlargement of thesize of the variable wavelength interference filter 5 larger compared tothe amount of the enlargement of the size of the effective measurementarea, such that the it is required to double the filter size in orderfor enlarging the effective measurement area G to have the size 1.5times as large as the original size, for example.

Further, in addition thereto, if the size of the variable wavelengthinterference filter 5 is enlarged, the electrical power for displacingthe movable section 521 is also increased, and it becomes also difficultto keep the stress balance of the holding section 522 even, andtherefore, the control for evenly displacing the movable section 521becomes also difficult.

In contrast, in the present embodiment, since the configuration ofmagnifying the transmitted light by the magnifying lens system 36 andthen receiving it by the detection section is adopted, it is notrequired to enlarge the size of the variable wavelength interferencefilter 5, and the variable wavelength interference filter 5 having asmall size with respect to the detection section 32 can be used.

Action and Advantages of Fourth Embodiment

As described above, in the optical device 1C according to the fourthembodiment, the magnifying lens system 36 is disposed between thevariable wavelength interference filter 5 and the detection section 32.Therefore, the size of the detection section 32 can be enlarged withoutenlarging the size of the variable wavelength interference filter 5.Therefore, the problem of degradation of the resolution, increase in thepower consumption, control of the movable section 521, and so on due tothe increase in size of the variable wavelength interference filter 5does not arise, and the highly accurate spectral distributionmeasurement can easily performed using the detection section 32 having alarge size.

Other Embodiments

It should be noted that the invention is not limited to the embodimentsdescribed above, but includes modifications and improvements within arange where the advantages of the invention can be achieved.

For example, although in the first embodiment the configuration diagramhaving an aperture disposed inside the telecentric optical system 31 isshown in FIG. 2, the invention is not limited thereto. The lens groupconstituting the telecentric optical system 31 can be composed of anyoptical members providing the incident light within the field anglerange, which can be imaged by the optical device 1, is collected in theeffective measurement area G, and the principal rays thereof areparallel to each other, and input perpendicularly to the variablewavelength interference filter 5, and the number and types of theoptical members are not limited. For example, the telecentric opticalsystem having the configuration shown in FIG. 10 can also be provided.

Further, although in the embodiments described above, the electrostaticactuator 54 for displacing the movable section 521 while deflecting theholding section 522 in response to the voltage applied between the firstelectrode 541 and the second electrode 542 is described as an example ofthe gap varying section, the invention is not limited thereto.

For example, it is also possible to adopt the configuration of using adielectric actuator disposing a first dielectric coil instead of thefirst electrode 541, and disposing a second dielectric coil or apermanent magnet instead of the second electrode. For example, in theconfiguration of disposing the first dielectric coil and the permanentmagnet, the magnetic force is generated using the current flowingthrough the first dielectric coil as the input value, and the movablesection 521 is displaced due to the attractive force or the repulsiveforce generated between the first dielectric coil and the permanentmagnet.

Further, it is also possible to adopt the configuration of using apiezoelectric actuator instead of the electrostatic actuator 54. In thiscase, for example, a lower electrode layer, a piezoelectric film, and anupper electrode layer are disposed on the holding section 522 in astacked manner, and the voltage applied between the lower electrodelayer and the upper electrode layer is varied as an input value, andthus the piezoelectric film is expanded or contracted to thereby deflectthe holding section 522.

Further, it is also possible to adopt the configuration of using anactuator utilizing pneumatic pressure instead of the electrostaticactuator 54. In this case, the space between the first substrate 51 andthe second substrate 52 is formed as an enclosed space, and an airinduction hole for introducing the air into the enclosed space isprovided. Further, a pump for varying the inside air pressure isprovided to the air induction hole, and the air pressure is varied as aninput value to thereby displace the movable section 521 due to thevariation in the internal pressure.

Further, although in the embodiments described above the holding section522 shaped like a diaphragm is described as an example, it is alsopossible to adopt a configuration of, for example, providing a pluralityof holding sections having a beam structure, and holding the movablesection 521 with these holding sections having the beam structure. Inthis case, it is preferable to provide the holding sections symmetricalabout the center axis O in order for making the deflection balance ofthe holding sections having the beam structure even.

Further, although in the embodiments described above there is shown theexample of the variable wavelength interference filter having theconfiguration in which the inter-reflecting film gap between the firstreflecting film and the second reflecting film is smaller than theinter-electrode gap between the first electrode and the secondelectrode, it is also possible to adopt the configuration in which theinter-reflecting film gap and the inter-electrode gap have the samedimension. Further, it is also possible to adopt the configuration ofthe variable wavelength interference filter in which theinter-reflecting film gap is larger than the inter-electrode gap.

Further, although there is described the configuration provided with thefirst circularly polarizing plate 34 in the second embodiment, and theconfiguration provided with the first circularly polarizing plate 34 andthe second circularly polarizing plate 35 in the third embodiment asexamples, it is also possible to adopt the configuration, for example,not provided with the first circularly polarizing plate 34, but providedonly with the second circularly polarizing plate 35. Further, althoughin the fourth embodiment there is described the configuration providedwith the first circularly polarizing plate 34 and the second circularlypolarizing plate 35 as an example, it is also possible to adopt theconfiguration provided with either one of the first circularlypolarizing plate 34 and the second circularly polarizing plate 35, orthe configuration not provided with the first and second circularlypolarizing plates 34, 35, for example.

Further, although in the third embodiment described above, there isadopted the configuration provided with the ¼-wave plate 351 facing tothe variable wavelength interference filter 5 and the linearlypolarizing plate 352 facing to the detection section 32 as the secondcircularly polarizing plate 35, the invention is not limited thereto.For example, it is also possible for the second circularly polarizingplate 35 to have the configuration provided with the linearly polarizingplate facing to the variable wavelength interference filter 5 and the¼-wave plate facing to the detection section 32.

In this case, the linearly polarizing plate transmits, for example, theP-polarized wave and absorbs the S-polarized wave out of theright-handed circularly polarized wave transmitted through the variablewavelength interference filter 5. Further, the P-polarized wavetransmitted through the linearly polarizing plate is converted by the¼-wave plate into the right-handed circularly polarized wave, and isemitted toward the detection section 32. Further, the light componentreflected by the detection section 32 has been converted into theleft-handed circularly polarized wave due to the reflection, and istherefore converted by the ¼-wave plate into the S-polarized wave, andis absorbed by the linearly polarizing plate.

Besides the above, specific structures and procedures to be adopted whenputting the invention into practice can arbitrarily be replaced withother structures and so on within the range in which the advantages ofthe invention can be achieved.

The entire disclosure of Japanese Patent Application No. 2010-254066,filed Nov. 12, 2010 is expressly incorporated by reference herein.

What is claimed is:
 1. An optical device comprising: a variablewavelength interference filter that include an effective measurementarea and that transmits a first light reinforced by multipleinterference out of an incident light; a telecentric optical system thatguides the incident light to the variable wavelength interferencefilter; and a detection section that detects a second light transmittedthrough the variable wavelength interference filter, wherein thevariable wavelength interference filter includes a first substrate, asecond substrate opposed to the first substrate and provided with amovable section, and a holding section that holds a periphery of themovable section and that holds the movable section so as to allow a backand forth movement of the movable section with respect to the firstsubstrate, a first reflecting film provided to the first substrate, asecond reflecting film provided to the movable section, and opposed tothe first reflecting film via a gap having a center gap and a peripheralgap, and a gap varying section that displaces the movable section tothereby vary a dimension of the gap, the telecentric optical systemguides a principal ray of the incident light perpendicularly to one of aplane of the first reflecting film and a plane of the second reflectingfilm, and collects the incident light in the effective measurement areaof the variable wavelength interference filter, a center, which has thecenter gap when the movable section is displaced with a maximum amountby the gap varying section, of the effective measurement area is in acentral axis of the movable section, and a periphery, which has theperipheral gap when the movable section is displaced with the maximumamount by the gap varying section, of the effective measurement area isin a peripheral area of the first and second reflecting films, and a gapdifference between the center gap and the peripheral gap is within apredetermined nanometric range.
 2. The optical device according to claim1, wherein the effective measurement area is capable to transmit thesecond light that has a predetermined allowable range of a wavelength,and when the movable section is displaced with the maximum amount by thegap varying section, the gap difference is equal to or smaller than ahalf of the predetermined allowable range.
 3. The optical deviceaccording to claim 1, further comprising: a magnifying lens systemdisposed between the variable wavelength interference filter and thedetection section, and adapted to magnify the second light transmittedthrough the variable wavelength interference filter.
 4. The opticaldevice according to claim 1, further comprising: a first circularlypolarizing plate that is disposed between the telecentric optical systemand the variable wavelength interference filter, that transmits thefirst light proceeding from the telecentric optical system toward thevariable wavelength interference filter, and that absorbs a firstreflected light proceeding from the variable wavelength interferencefilter toward the telecentric optical system.
 5. The optical deviceaccording to claim 1, further comprising: a second circularly polarizingplate that is disposed between the variable wavelength interferencefilter and the detection section, that transmits the second lightproceeding from the variable wavelength interference filter toward thedetection section, and that absorbs a second reflected light proceedingfrom the detection section toward the variable wavelength interferencefilter.
 6. The optical device according to claim 1, wherein thepredetermined nanometric range of the gap difference is 2.5 nm to 5.0nm.